Devices such as cranes, have lateral outriggers with hydraulically projected pads which engage the ground to keep the crane stable while in use. Since the hydraulically projected pads require pumped hydraulic fluid only when being projected, there is hydraulic pumping capacity available for other uses after the crane, or other device, has been stabilized.
In cranes, it is proposed to use a diverter valve for selecting two functions the flows of which are combined to achieve maximum operating efficiency of a single winching function. This requires a solenoid operated, three-way valve which in a satisfactory configuration is currently not available. Current three-way valves malfunction because they utilize a solenoid spool which is subject to Bernoulli forces.
In presently available three-way spool valves, malfunctions occur as certain flow limits are passed, during high pressure conditions, or when high flow rates combine with high pressure conditions. In order to cope with this phenomenon, attempts have been made to increase the size of three-way valves. However, as size increases, design difficulties are encountered because it is necessary to match available solenoid forces against a required spring force to overcome Bernoulli forces. Bernoulli forces occur when two negative flows caused by the velocity of hydraulic fluid over flow surface areas of the spool combine, creating a negative force which tends to close the valve spool. One approach to solving this problem has been to use solenoid-operated, four-way valves to perform the function of three-way valves. However, since four-way valves are of essentially the same design configuration as three-way valves, they also fail under Bernoulli forces. Another approach has been to use various combinations of bi-directional, two-way valves, but this requires two separate solenoid valves and it is preferable to utilize only a single solenoid valve. Use of two-way valves in combination is also not necessarily desirable because the two-way valves can sometimes stall or restrict flow if certain differential pressure conditions are not met.